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IS 3025-22 (1986) : Methods of Sampling and Test (Physical 
and Chemical) for Water and Waste Water, Part 22: Acidity 
[CHD 32: Environmental Protection and Waste Management] 




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UDC 628-1/3: 543-31 9 



IS: 3025 (Part 22) -1986 




Indian Standard 

METHODS OF SAMPLING AND TEST 

(PHYSICAL AND CHEMICAL) 

FOR WATER AND WASTE WATER 

PART 22 ACIDITY 

( First Revision ) 



( Reaffirmed 2003 ) 



1. Scope — Prescribes the indicator and potentiometric methods for determination of acidity. These 
methods are applicable to the determination of acidity in water and waste water. The applicable range 
Is 0-5 to 500 mg/l ac\6\Xy as CaCOg. 

2. Principle and Theory — Acidity of water is its quantitative capacity to react with a strong base 
to a designated pH. It may be defined as equivalent concentration of hydrogen ions in mg/l. The 
equation in its simplest form is as follows: 

H+ + NaOH =- HgO -f Na+ 

3. Interferences — A fading and temporary end point characterizes the phenolphthalein acidity 
titration performed at room temperature on a sample containing iron and aluminium sulphate. Better 
results are obtained by titrating the sample at boiling temperature. Acid samples from mine drainage 
are subjected to interferences. Coloured or turbid samples may Interfere in end point. Analyse such 
samples by potentiometric titration. 

4. Sampling and Storage — Sampling and storage shall be done as prescribed in IS : 3025 (Part 1 )- 
1986 'Methods of sampling and test (physical and chemical) for water and waste water: Part 1 
Sampling ( first revision )'. 

5. Sample Preparation — The test sample used should be free from turbidity or filtered through 
0-45 ^m membrane filter. 

6. Apparatus 

6.1 pH IVIeter 

6.2 Burette — 5Q'r[\\ capacity. 

6.3 Magnetic Stirring Device 

7. Reagents 

7.1 Distilled Water — pH should not be less than 60. If the pH is less than 60, it shall be freshly 
boiled for 15 minutes and cooled to room temperature. Deionlzed water may be used provided that it 
has a conductance of less than 2 /^s/cm and a pH more than 6-0. 

7.2 Potassium Acid Phthalate — 0-02 N. Dissolve 40846 g of potassium acid phthalate salt (KHCgH^O^) 
( dried at 120''C for 2 hours ) in carbon dioxide free distilled water and dilute to 1 litre. 

7.3 Sodium Hydroxide Solution --^5 N. 

7.3*1 Sodium hydroxide solution — I N. Dilute 67 ml of 15 N sodium hydroxide solution (7.3) to 
one litre with distilled water. 

7.3.2 Sodium hydroxide solution — 0-02 N. Dilute 20 ml of 1 N sodium hydroxide solution (7.3.1 ) 
to one litre and standardize using standard potassium acid phthalate (7.2). 

7.4 Phenolphthalein Indicator — DlssoWe 0-5 g of phenolphthalein In 100 ml, 1:1 ( vjv) alcohol water 
mixture and add 0-02 N sodium hydroxide solution drop by drop till very faint pink colour Is observed. 

7.5 Methyl Orange Indicator ^ DlssoWe 0-5 g of methyl orange In distilled water and make up to 
100 ml in a volumetric flask. 



Adopted 31 July 1986 



February 1987, ISI 



Gr 1 



INDIAN STANDARDS INSTITUTION 

MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG 

NEW DELHI 110002 



IS: 3025 (Part 22) -1986 

8. Procedure 

8.1 Indicator Method — Pipette 20 ml or a suitable aliquot of sample Into a 100-ml beaker. The sample 
size shall be so selected so that not more than 20 ml of titrant Is needed for the titration. Determine 
the pH of water. If pH is less than 3-7, add two drops of methyl orange indicator into the first sample 
beaker and titrate with standard 002 N sodium hydroxide solution until the colour changes to the faint 
orange characteristic of pH 3-7. Record the volume of sodium hydroxide used. To the second sample 
beaker, add 2 to 3 drops of phenolphthalein indicator and titrate with 0-02 N sodium hydroxide solution 
to the appearance of faint pink colour characteristics of pH 8*3. Record the volume used. 

8.2 Potentlometric Method — Pipette 20 ml or a suitable aliquot of sample into a 100-ml beaker. 
Titrate with standard sodium hydroxide solution to pH 3-7 and pH 8*3. Record the volume of standard 
sodium hydroxide used. No Indicator is required. 

9. Calculation — Calculate acidity In the sample as follows: 

Acidity at pH 3*7, as mg/l CaCOg 



A 


X 


N 


X 


50 000 








V 




B 


X 


N 


X 


50 000 



Acidity at pH 8-3, as mg/l CaCOg = 

where 

A — volume In ml of standard sodium hydroxide used to titrate to pH 3-7, 

N = normality of standard sodium hydroxide, 

V = volume In ml of sample taken for test, and 

B = volume In ml of standard sodium hydroxide used to titrate to pH 8-3. 



EXPLANATO RY NOTE 

Acidity of water or waste water is its quantitative capacity to react with a strong base to a 
designated pH. Strong mineral acids, weak acids like acetic and carbonic and hydrolyzable salts like 
ferrous or aluminium sulphates may contribute to the measured acidity. Adds contribute towards 
corrosiveness, influence chemical reactions and biological processes. The measurement also reflects 
a change in the quality of the source water. 

This method supersedes 19 of 13:3025-1964 'Methods of sampling and test (physical and 
chemical ) for water used in industry'. 



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